This invention relates to an environmental control system and a method of employing same to control both the temperature and humidity of a controlled space, such as a poultry house.
It is well known that to optimize the health, growth rate and production of farm animals, such as chickens, contained in agricultural enclosures, such as poultry houses, it is necessary to control both the temperature and the relative humidity. Accordingly, as shown in U.S. Pat. No. 3,511,299, entitled "Condition Responsive Closure Operating Device", and assigned to the asignee of this invention, it is known to provide automatic ventilation systems which are controlled to provide increased ventilation/cooling on an override basis in response to excess humidity. Ventilation/cooling is operated until either a desired relative humidity level is attained or a minimum selected temperature is reached.
Similarly, it is known to over-cool air with an air conditioning unit to reduce humidity by removing moisture from the air through condensation. For instance, in U.S. Pat. No. 4,290,480 of Sukowski and entitled "Environmental Control System", an air conditioning unit is actuated to reduce relative humidity. If this also reduces the temperature below a preselected limit, then heaters controlled by a thermostat are operated concurrently with the cooling air conditioning.
Multiple stage controllers are also known such as shown in U.S. Pat. No. 3,714,980 of Lancia et al. in which multiple humidifiers and dehumidifiers are caused to operate at different humidity levels while independent controllers responsive to temperature only cause heaters/coolers to operate.
Environmental thermostatic control systems are also known in which both heaters and coolers are controlled in accordance with temperature alone. Such a system may have established "dead zones" of temperature during which neither heaters nor coolers are actuated as in the system shown in U.S. patent application Ser. No. 06/584,398 of Alfred T. Newell III et al., filed Feb. 28, 1984, and entitled "Electronic Thermostat" and assigned to the assignee of this invention.
A problem with the systems which operate ventilation/cooling apparatus concurrently with heaters, is that they are wasteful of energy. In a poultry house in which excessive relative humidity is caused by to moisture from the birds, ventilation alone will reduce relative humidity if the relative humidity of the fresh air is lower than that of the humid air within the enclosure at the outside ambient temperature. However, relative humidity can also be lowered simply by raising the temperature, but this natural beneficial effect is reduced by continuing ventilation after heaters have begun to operate.